Radio navigational aid



Jan 2, 1951 E. FENNEssY 2,536,433

RADIO NAvIGATIoryI'AL AID Filed May 13, 1947 2 Sheets-Sheet l E. FENNESSY RADIO NAVIGATIONAI.l AID Jan. 2, 1951 Filed May 15, 1947 2 Shegts-Sheet 2 Patented Jan. 2', 1951 UNITED STATES PATENT OFFICE RADIO NAVIGATIONAL AID Edward Fennessy, Orpington, England, assignor to The Decca Record Company, Limited, London, England, a corporation of Great Britain Application May 13, 1947, Serial No. 747,660

In Great Britain May 17, 1946 l6 Claims.

This invention relates to radio navigational aids and has particular reference to a radio frequency transmitting and receiving system for indicating continuously the geographical location of a mobile vehicle.

In a co-pending application oi William J. OBrien Serial Number 612,987 filed August 27, 1945 entitled Navigation System now abandoned and assigned to the assignee of this application, there is described a radio frequency navigational system for aiding the navigation of mobile vehicles. The system referred to employs a master transmitting apparatus and at least two slave transmitters operating simultaneously to continuously radiate at least three signals of different but harmonically related frequencies which are maintained in a Xed multiple phase relation to each other.

The mobile receiving apparatus comprises means for separately receiving the radiated signals, frequency converting apparatus for producing from the received signals at least two pair of equal frequency signals, and phase indicators for measuring and continuously indicating the phase relation between the reference signals of each pair.

The transmitting apparatus may, for example, operate on the sixth, eighth and ninth harmonics of a selected fundamental frequency. In the receiving apparatus a pair of twenty-fourth harmonic reference signals are derived from the received sixth and eighth harmonics, and a pair of eighteenth harmonic reference signals are similarly derived from the sixth and ninth harmonics. In the example chosen, the transmitting t apparatus thus operates to establish two overlapping equi-phase displacement eld patterns, one at the eighteenth harmonic frequency, and one at the twenty-fourth harmonic frequency. The receiving apparatus operates to continually indicate the location of the mobile vehicle in terms of the two equi-phase displacement field contours thus established.

With a system of the character described using requencies of the order of magnitude of 100 kc., a position fix with an error not exceeding a few yards is readily obtained in that portion of the area served by the system which lies in the near vicinity of the transmitters. However, since the eld patterns are hyperbolic, the accuracy reduces as the distance from the transmitters is increased, due in part to the divergence of the equi-phase lines, and in part due to the acuteness with which the lines of one pattern intersect those of the other. It follows that in the near vicinity of the transmitters the accuracy is sufcient for airport approaches, and for river and harbour navigation, while at distances of about 3Go miles, the accuracy is not sufficiently high to meet the exacting requirements of such navigational problems.

it is therefore an object of this invention to provide an improved navigational system for use in conjunction with a system of the character referred to and which operates to provide high accuracy in relativey local areas in which the overall system accuracy is low.

It is another object of this invention to provide a navigational system of the character described in the preceding paragraph which employs at said local areas short range very high frequency transmitting apparatus operating to radiate signals modulated at unlike but harmonically related frequencies, and in which said modulation frequencies bear a fixed multiple phase relation to each other.

It is also an object of this invention to provide a navigational system of the character set forth in the preceding paragraph in which said modulation frequencies are identical to the radio frequency signals used to establish the overall navigational pattern.

It is a still further object of this invention to provide an improved navigational system of the character hereinbefore referred to which includes a receiving apparatus arranged to selectively receive directly the signals of said overall pattern, or alternatively to receive and dcrnodulate said very high frequency modulated signals.

It is also an object of this invention to provide a receiving apparatus of the character set forth in the preceding paragraph in which the same phase measuring and indicating equipment is used with either set of signals.

Other objects and advantages of this invention will be apparent from a consideration of the following description read in connection with the accompanying drawings wherein:

Fig. 1 is a diagram illustrating the manner in lwhich the auxiliary system of this invention opcrates to increase the accuracy of position indication within a relatively local area;

Fig. 2 is a block diagram illustrating the master and slave transmitting equipment comprising the auxiliary system represented in Fig. l; and

Fig. 3 is a block diagram of a receiving apparatus which may be used alternatively with the overall system or with the auxiliary system forming the subject matter of this invention.

Referring to the drawings I have illustrated in Eig. 1 a, portion oi' a map or chart oi' an area by an overall navigational system such as that disclosed in the aforementioned co-pending applicatlon Serial lwumbe'r 612,987. The local area 'represented m Fig. 1 is considered to be situated a considerable distance from the transmitting apparatus or the overall system and may comprise an area within which high accuracy of position indication is extremely desirable. area may include a shore line such as represented at i and which is indented as shown at 2 'and t to define a bay or estuary. The estuary may comprise a port or harbour within lwhich it is desired to navigate surface ships with considerable accuracy. However, because of its distance from the transmitting apparatus of the overall system, the accuracy afforded by that system may be relatively low due to the relatively wide 'spac ing between the equi-phase contours and due also to the actute angie which the contours of one co-ordinate makes with the contours of the other. Such a relatively inaccurate form of coverage is represented by the dotted lines in Fig. 1 in which the dotted lines d represent the equiphase contours of one co-ordinate and in which the ydotted lines represent the equi-phase contours of the other co-'ordinate According to this invention the accuracy of positional fix within the estuary is greatly increased by using a relatively short range very high frequency auxiliary navigational system which may comprise a master transmitter at location A and slave transmitters at locations B and C. These transmitters operate to establish two overlapping sets of equi-phase field contours such as are represented in Fig. 1 by the solid vlines ii and l.

The overall navigational pattern 4, E may be assumed to be established by means of transmitters operating on sixth, eighth and ninth harn m'oriics of a given fundamental frequency as, for example, frequencies of 60, 8O and 90 kc. According to this invention the auxiliary apparatus at locations A, vIB and C operates at a very high frequency of the order of magnitude of 40 megacycles or more and is amplitude modulated 'at the same frequencies als are used to establish the overall pattern l, '5. According to the vassumed example the signals radiated from locations A, B and C will therefore be modulated at fre quencies of 69, 80 and 90 Ykc. respectively. The spacing between the locations A, B and C may She selected as desired with a View to disposing the field contours and 'i in the most advantageous arrangement with respect to Vthe local area to be served by the auxiliary system, namely, the estuary Vdefined by the shore lines 2 and 3.

In Fig. 2 there is illustrated by means of a block diagram transmitting apparatus which may be employed for establishing the auxiliary navigational pattern. The master transmitter which is situated at location A may 'comprise a source of very high radio frequency energy such as an oscillator Hl. to any desired very high frequency as, for example, a frequency of 40 megacycles. IThe oscillator it is coupled to a power amplier il which feeds a modulator l2, the modulator being coupled in any suitable manner to a transmitting antenna i3 situated at location A. There is also employed an oscillator le or signal generator which is tuned to the sixth harmonic 'of the 4given fundamental frequency ubon which the navigational pattern is based. In accordance The This oscillator may be tuned with the assumed example the oscillator l is tuned to o0 Kc. The oscillator lli is coupled to an ampliller le the output 0I- Which is applied to the modulator l2 so that the slgnals radiated from the antenna i3 comprises lu mcgacycle signals amplitude modulated at a frequency of 6() kcS.

fine slave transmitting apparatus which is situated at location B comprises a means for Vraulatlng high frequency signals of a frequency different from those radiated from location A together with means for modulatlng those signais at the eighth harmonic of the selected fundamental lrequency and together with means for' maintaining a fixed multiple phase relation between the 80 kc. modulation andthe 50 kc. modulation originating at location A. The slave transmitter' B may accordingly comprise a source or' very h g'n frequency energy such as an oscil lator i6 tuned, for example, to a frequency of 49.5 megacycies. The output 'of the Ioscillator 'lil 'is 'coupled to the power amplifier Il' which in turn reeds a modulator i8. The modulator 'i8 is coupled in va vsuitable manner toa transmitting antenna it which is situated 'at location B.

l In order to maintain the required fixed multiple phase relatlon between the 80 kc. modulationsighal from location E and the '60 kc. modulation signal from location A, the 80 kc. signal is derived -irom 'the 60 kc. signall To this end there -is employed at llocation B a receiving antenna 2Q which is coupled to a radio frequency receiver y2i tuned to ed megacycles so as to receve the very high frequency signal radiated from antenna i3 at location A. The output of the receiver 2i is applied to -a detector circuit -2'2 which serves to de-modulate the received signal and produce a kc. output. This '60 kc. output is fed as indicated at 23 toa divider 2d operating to :produce a 4'20 kc. output signal. The -20 kc. output signal is passed through a phase -controller t vto a frequency multiplier 2E lwhich operates to produce from the V20 kc. input "an Solac. output signal. The vSi) kc. outputs'ig-nal is amplied by means -of an a'irfplici 2l coupled to the modulator i8 so as to modulate at 80 kc. the 40.5`meg'ae cycle signal radiated from antenna i9.

A portion 'of the 60 kc. output of the Adetector 22 is applied as indicated at '28 to a frequency multiplier 'circuit 29 which operates to produce a 21i0 kc. Voutput signal. This output signal is applied to one input circuit of a phase discrimi-` nator Sii. The other input to the phase vdiscriminator circuit is derived from a pick-up loop Si positioned near th'e circuit of antenna i9 so as to be "excited at 'the 'radiated frequency of 49.5 megacycles. The small signal thus induced in the loop 'Si 'is 'applied to a 40.5 megacycle amplifier "32 the output of which is connected to a detector 33. The detector 33 operates to demodulate the input signal and so produce an output signal having a frequency of kes. This 80 kc. signal is passed to a frequency multiplier 315i which operates to vproduce a 240 kc. 'output signal which is applied to the 'other input circuit of the phase discriminator l30.

The phase discr'irfiinator 3B may be of any suitable' type but a preference is expressed for a phase dis'criminator Vcircuit of the 'character disclosed in a c'o-pending application led :by WiliarnJ. OBrien Serial Number 612,991 filed August 27, 1945 and entitled Multiple Channel Radio Frequency Receiver, now Patent No. 2,590,200 issued March 14, 1950.

The phase discriminate-r circuit described in the above identiiied application operates to compare the phase of two input signals of like frequency (in this case the two 240 kc. signals from the multipliers 2S and 34) and produce a direct control potential the magnitude and polarity of which is a function of the phase relation between the two input signals. This direct control potential is applied as indicated at to the phase controller 25.

Any suitable form of phase controller 25 may vbe employed but a preference is expressed for the phase regulating circuit .disclosed in a c0- pending application filed by William J. OBrien Serial Number 612,985 filed August 27, 1945 and entitled Radio Frequency Transmission Apparatus, now abandoned. The phase controller which is described inthe above identified application includes a tuned circuit having connected thereto a thermionic vacuum tube connected in a reactance circuit so that the tuned circuit may be slightly cle-tuned by varying the grid bias of the thermionic tube. This grid bias shift is derived from the variations in the direct control potential produced by the phase discriminator 30.

The apparatus is so arranged that whenever the phase of the 80 kc. modulation signal radiated from antenna i9 shifts from a normal relationship with respect to the received kc. modulation signal the resulting change in the direct control potential produced by the phase discriminator 36 will so control the operation of the phase controller 25 as to introduce into the 80 kc. signal a phase shift in a direction tending to restore the multiple phase relation between the 60 and 80 kc. signals to the desired ncrmal. It will be seen that the equipment thus operates as a phase regulator to maintain a xed and unchanging phase relation between the 60 and 86 kc. modulation envelopes.

The apparatus comprising the slave transmitter situated at location C is identical to that de-I scribed at location B except that the carrier frequency employed is different from the master or first slave carrier frequency and may be, for example, 4l megacycles. Also the modulation frequency used is 90 kc. and the phase comparison for phase controlling purposes is made on the basis of a frequency of 180 kc.

It Will be seen that the transmitting' apparatus just described operates t0 radiate from locations A, B and C three unlike radio frequency signals of very high :frequency and that these signals are modulated at frequencies corresponding to the sixth, eighth and ninth harmonics of a selected fundamental frequency. It will be appreciated that by reason of the very high frequency used as a carrier frequency the range of the auxiliary system is relatively short, the carrier frequencies being chosen with a view to limiting the ground wave to relatively short distances and with a view to eliminating sky wave reflections. It will thus be seen that within the area served by the overall navigation system short range systems of the type described for the purpose of creating over certain areas an equiphase displacement field pattern of materially higher accuracy than is established in that area by the overall navigation system. These separate systems may operate independently of each other and because of their very short range characteristic introduce no problems concerning interference or overlapping.

In Fig. 3 there is illustrated a receiving apparatus which may be used alternatively with the overall navigational system and with the various auxiliary systems such as just described. For use with the overall navigational system there is employed a receiving apparatus such as that described in the afore-mentioned co-pending application Serial Number 612,991 which may include a receiving antenna 36 suitable for receiving the radio frequency signals comprising the overall navigational system. The antenna 36 is connected to corresponding contacts 3l, 38 and 39 of a three pole double throw switch 40. One blade 4| of the switch is connected to an amplier 42 tuned to one of the received frequencies as, for example, kc.; a second blade 43 is connected to an amplifier 44 which may be tuned to 60 kc.; and a third switch blade 45 is connected to a third amplifier 46 which may be tuned to the remaining frequency of lic. The output of the amplier 42 is fed to a frequency multiplier 41 operating to produce a 240 kc. output signal which is fed to one input of a phase discriminator 48. The output of the 60 kc. amplier 44 is coupled as indicated at 49 to a frequency multiplier '50 which produces a second 240 kc. output signal, the second 240 kc. signal being connected to the second input circuit of the phase discriminator 48. The phase relationship between the two 240 kc. signals measured and determined by the phase discriminator 48 is indicated on a suitable phase indicator 5! coupled to the discriminator 4S. Similarly the 90 kc. output of the amplifier 46 is doubled to a frequency of kc. in a frequency multiplier 52 which feeds one input circuit of another phase discriminator 53. The output of the 60 kc. ampliiier 46 is connected as shown at 54 to a frequency multiplier 55 which produces a second 180 kc. signal which is fed to the second input circuit of the phase discriminator 53. The phase relation between the two 180 kc. signals is indicated by a phase indicator 56 coupled to the phase discriminator 53.

While any suitable form of phase indicator for the indicators 5l and 56 may be employed, a preference is expressed for a phase indicator of the character disclosed in co-pending application led by William J. OBrien Serial Number 612,984 led August 27, 1945 and entitled Registering Goniometer, now Patent No. 2,499,326 issued February 28, 1950.

The apparatus just described with the switch 40 thrown to position connecting amplifiers 42, 44 and 46 to the receiving antenna 36, is identical to the receiving apparatus shown in the aforementioned co-pending application Serial Number 612,991.

In addition to the apparatus just described the receiving apparatus of this invention includes a second receiving antenna 51 of a type suitable for the receiving of Very high frequency signals such as are radiated from the aforementioned locations A, B and C. This antenna is coupled to three very high frequency amplifiers 58, 59 and 60 tuned respectively to the three carrier frequencies radiated from locations A, B and C that is, to frequencies of 40.5, 40.0 and 41.0 megacycles. The output of each of the amplifiers 58, 59 and 60 is connected to corresponding detector circuits 6|, 62 and 63 which operate to de-modulate their respective input signals and provide output signals of 80, 60 and 90 kc. The output of the detector circuits 5l, 62 and 63 are connected to contacts 64, 65 and 66 of the three pole double throw switch 40. With this arrangement the switch 40 may be thrown to a position alternative to that hereinbefore described so as to connect the -detector circuits 6|, 62 and 63 to the input circuits of the amplifiers t2, 4d and 46.

It will be appreciated that when the switch is thrown to the alternate position the 80, 60 and 9G kc. signals from the detector circuits tl, t2 and 63 will be handled by the remainder of the receiving apparatus in exactly the same way as when the 80, 60 and 90 kc. radio frequency signals are derived from the receiving antenna 36.

In accordance with the intended mode of operation, a receiver of vthe character illustrated in Fig. 3 carried by a surface ship orv aircraft will normally be operated With the amplifiers d2, 44 and 4E connected to the receiving antenna 36 so that the navigation of the vehic e will be guided by the overall navigational system. When, however, the ship or aircraft approaches a harbour or airport tted with the auxiliary system described in this specification, the switch d is thrown to the alternative position so as to provide positional data with reference to the alternative navigational pattern established by the auxiliary system. It will be seen that the amount of additional receiving equipment which must be carried by a surface ship or aircraft in order to take advantage of the facilities oered by such an auxiliary system is very small indeed, it being appreciated that the very high frequency amplier and detector circuits may be made of smal light Weight components and so assembled as an I' inexpensive and light Weight unit.

In the foregoing kthere has been described an improved navigational system using auxiliary sets of transmitting apparatus which may 4provide short range navigational signals providing greatly improved accuracy in certain local areas Where such improved accuracy is highly desirable. It Will be observed also, that the system described includes auxiliary receiving apparatus making it possible for a given ship or aircraft to use alternatively, and as desired, the navigational signals comprising an overall navigational pattern or those comprising a higher accuracy local auxiliary pattern. Attention is directed particularly to the very small amount of additional equipment required to adapt the mobile receiving apparatus for operation at will on either system.

Whiie there has been shown and described the preferred embodiment of this invention the same n, is not to be limited to the details illustrated .and

described herein except as dened in the appended claims.

I claim:

l. In a radio frequency navigational aid, the combination of: transmitting .means at spaced points for simultaneously radiating .from said points very high radio frequency energy at dif.- ferent frequencies; means at each of said transmitting means for modulating each of said very high radio frequency radiations at a different modulation frequency, said different modulation frequencies being harmonically related; and means for maintaining a xed multiple phase relation among said modulation frequencies.

2. ,In a radio frequency navigational aid, the combination of: transmitting means at spaced points for simultaneously radiating from said points very high radio frequency energy at different frequencies; means at each of said transmitting means for amplitude modulating each :of said very high radio frequency radiations at a different modulation frequency, said different modulation frequencies being harmonically related; and means for maintaining .a Vfixed mul- 8. tiple phase relation among said modulation frequencies.

3. In a radio frequency navigational aid, the combination of: transmitting means kat spaced points for simultaneously radiating from `said points radio energy of different lfrequencies each in excess of thirty megacyclcs per second; means at each of said transmitting means for modulating each of said very highV radio frequency radiations at a different modulation frequency, said different modulation frequencies being harmonically related; and vmeans for maintaining a fixed multiple phase relation among ksaid modulation frequencies.

4. In a radio frequency navigational aid, the combination of: transmitting means at spaced points for simultaneously radiating from said points very high radio frequency energy at different frequencies; means at each of said transmitting means for modulating said very high radio frequency radiations at a different modulation frequency, said diierent modulation frequencies being harmonically related; means for maintaining a fixed multiple phase relation among v niodulation frequencies; receiving means for simuitaneously receiving said radiations; means at said receiving means for demodulating the received radi-ations to producc1 output signals having different modulation frequencies; and means for measuring and continuously indieating the muitiple phase relation among said output signals.

5. In a radio frequency navigational aid, the combination of a master transmitter for radiating a very high radio frequency signal modulated at a master modulation frequency; a pair of slave transmitters spaced from said master transmitter and spaced from each other for radiating very high radi-o frequency signals of different frequcncies each different than the signal radiated by said master transmitter and each modulated at 4different slave modulation frequencies each bearing 'a harmonic relation to said master modulation frequency; and means at each of said slave transmitters for maintaining a fixed multiple phase relation between said slave modulation frequencies and said master modulation requency.

l6. In a radio frequency navigational aid, the combination of means at spaced points for radiating three radio frequency signals of different but harmonicaliy related navigation frequencies bearing a fixed multiple phase relation yto each other for defining an over-all navigational pattern of intersecting equi-phase displacement Vfield contours; means for radiating from three other spaced points very high frequency radio energy of unlike frequency modulated at said navigation frequencies and With said modulations bearing a xed multiple phase relation to each other for defining a local navigational pattern of intersecting equi-phase displacement iield contours; and a mobile receiving device comprising receiving means for separately receiving said radio frequency signals, Yreceiving and detecting means -for separately receiving and cle-modulating said very high frequency radiations, `apparatus for measuring and continuously indicating the multiple phase relationships among said navigation frequencies, and means for connecting said apparatus alternately to said receiving means and to said receiving and rectifying means, whereby said apparatus indicates the location of said mobile 9 receiving device alternately with reference to said Number over-all pattern and said local pattern. 2,144,203 EDWARD FENNESSY. 2,198,113 2,218,907 REFERENCES CITED 5 2,403,626 The following references are of record in the 2,408,773 me of this patent: 2,419,525

UNITED STATES PATENTS Number Name Date 10 Number 1,002,141 Fessenden Aug. 29, 1911 546,000 1,942,262 Shanklin Jan. 2, 1934 Name Date Shankln Jan. 17, 1939 Holmes Apr. 23, 1940 Donnelly et al. Oct. 22, 1940 Wolff et al. July 9, 1946 Goodall Oct. 8, 1946 Alford Apr. 29, 1947 FOREIGN PATENTS Country Date Germany Feb. 18, 1932 

